Punnett Square Calculator

A Punnett square is a visual grid diagram used in biology to predict the probability of offspring inheriting particular genotypes and phenotypes from a cross between two parents. It was named after geneticist Reginald Punnett.

To make a 2x2 Punnett square for a single trait (monohybrid cross), write one parent's two alleles along the top edge of the grid and the other parent's two alleles along the left edge. Fill in each cell by combining the corresponding column and row alleles. The resulting four cells represent the potential genetic combinations for the offspring.

Genotype refers to the actual genetic makeup or allele combination of an organism (such as AA, Aa, or aa). Phenotype refers to the physical expression or observable trait of that genotype (such as brown eyes or blue eyes).

A dominant allele (written in uppercase, e.g., 'A') is expressed even if only one copy is present (e.g., AA or Aa). A recessive allele (written in lowercase, e.g., 'a') is only expressed physically if two copies are inherited (e.g., aa) in the absence of a dominant allele.

Homozygous means an organism has two identical alleles for a trait (either homozygous dominant 'AA' or homozygous recessive 'aa'). Heterozygous means the organism has two different alleles for a trait ('Aa').

A monohybrid cross is a genetic cross between two parents that differs in only one specific trait. The standard cross of two heterozygous parents (Aa x Aa) yields a characteristic 3:1 physical ratio and a 1:2:1 genetic ratio in the offspring.